将环型横向剪切干涉仪置于两个镜头之间,由此设计出一种新型的离焦4f差分干涉仪,该干涉仪同时具有分离光路的剪切量和条纹空间频率分别可调的优点以及共光路结构的稳定性和易于调节的优点,使得在测量大密度梯度等离子体的密度分布时,可以在不降低空间分辨率的条件下仍保证干涉条纹可读.在DPF装置上进行了实验,获得了等离子体壳层的干涉图样,计算了等离子体的径向电子密度分布,在内电极端面上方测量到的最高电子密度约为1.2×10¹⁹ cm^-3,外围等离子体壳层的电子密度约为2×10¹⁸ cm^-3.

A new type of differential interferometer using a defocused 4f imaging system is described. The interferometer is stable and easy to adjust with a ring structure. The shear amount and fringe spacing can be adjusted independently with the defocused 4f design. High spatial resolution and readable fringes can be obtained simultaneously in dense plasma diagnosis. As an example, the DPF plasma was diagnosed by the 4f system. Interferograms were acquired at different time during pinch process. The radial distributions of local electron density were calculated. The maximum local electron density above the anode end was measured about 1.2×10¹⁹ cm^-3 and that of the outer plasma shell 2×10¹⁸ cm^-3 when plasma began pinching.